1. Field of the Invention
The present invention relates to a mold clamping method for a straight hydraulic mold clamping apparatus, which can be used for molding machines such as injection molding machines, die-cast machines, or the like.
2. Background Art
Straight hydraulic mold clamping apparatuses for accelerating the speed of opening or closing mold halves by reducing oil resistance of a mold clamping piston which moves inside a mold clamping cylinder is already known. The straight hydraulic mold clamping apparatus has two oil chambers, which are located in the front and the rear of the cylinder respectively and communicate with each other via passages drilled through the mold clamping piston inserted into the cylinder, as well as a disk valve in the rear oil chamber for closing or opening the passage, engaged movably in the axial direction with the perimeter of the rear of a mold clamping ram. The straight hydraulic mold clamping apparatus also has an valve operation oil chamber disposed at the section where the disk valve is engaged with the mold clamping ram.
In the straight hydraulic mold clamping apparatus with a built-in disk valve, rapid-moving cylinders, parallel disposed in the rear of the mold clamping ram or along the side of the mold clamping cylinder, performs the opening or closing of the mold by moving the mold clamping ram together with the mold clamping piston and the disk valve.
Besides, after the mold closing is completed, with the rapid mold closing speed caused by the rapid-moving cylinders slowed down to a low speed/low pressure operation, communication between the front and the rear oil chambers is shut down by closing the passages through the mold clamping piston by the disk valve, and the pressure within the rear oil chamber, to which mold clamping oil is supplied, is raised to generate a large mold clamping force.
According to the mold clamping method, the rear oil chamber, being expanded as the mold clamping piston moves forward, is filled with oil flowing in from the front oil chamber which is being shrunk. However, there is a difference between the expansion ratio of the rear oil chamber caused by the rapid movement of the mold clamping piston and the inflow ratio of the oil flowing into the rear oil chamber caused by pressure of the mold clamping piston onto the front oil chamber. The difference, which varies according to the mold closing speed, is usually in a state of negative pressure due to lack of oil in the rear oil chamber.
Therefore, oil supply to the rear oil chamber after completion of the mold closing takes a stepwise operation as follows:
firstly, the supplied oil is consumed for resolving the negative pressure, PA1 the oil is compressed and the compression amount is compensated, PA1 then pressure in the rear oil chamber is raised by the supplied mold clamping oil. PA1 a rapid-moving cylinder having a piston rod inside; PA1 a mold clamping cylinder comprising a mold clamping ram equipped in the cylinder, a mold clamping piston which partitions the inside of the cylinder into a front oil chamber and a rear oil chamber communicating with each other via a passage drilled through the piston, a disk valve for closing or opening the passage, engaged with the mold clamping ram at the rear oil chamber movably in the axial direction, an valve operation oil chamber disposed at the section where the disk valve is engaged with the mold clamping ram, a supply passage for supplying oil to the valve operation oil chamber, and a supply passage of old clamping oil disposed in the rear oil chamber; PA1 a fixed platen on which a mold half is mounted; and PA1 a movable platen on which another mold half is mounted, in which the piston rod is connected to the movable platen so that the movable platen can be moved to open or close the mold, and the mold clamping ram is connected to the movable platen so that the movable platen can be clamped, PA1 the mold clamping method comprising the steps of: PA1 closing the movable platen by the rapid-moving cylinders to close the mold halves and to transfer oil in the front oil chamber to the rear oil chamber via the passage being open; PA1 slowing down the rapid-moving cylinder for completion of the mold closing process; and PA1 starting supply of mold clamping oil via mold clamping oil supply passage to the rear oil chamber immediately before completion of slowdown of the rapid-moving cylinders to start raising the oil pressure for mold clamping force simultaneously with completion of the mold closing.
The result is such that even though the mold closing is performed at a high speed, it takes time to raise the mold clamping pressure after completion of the mold closing, and injection charge of resin into the mold must wait until the mold clamping force reaches a predetermined pressure. Thus it is difficult to shorten the mold clamping time when high cycle molding is expected and this is the problem to be solved.